github.com/vescale/zgraph@v0.0.0-20230410094002-959c02d50f95/expression/constant.go (about)

     1  // Copyright 2023 zGraph Authors. All rights reserved.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package expression
    16  
    17  import (
    18  	"github.com/vescale/zgraph/datum"
    19  	"github.com/vescale/zgraph/stmtctx"
    20  	"github.com/vescale/zgraph/types"
    21  )
    22  
    23  var _ Expression = &Constant{}
    24  
    25  // Constant represents a literal constant.
    26  type Constant struct {
    27  	Value datum.Datum
    28  }
    29  
    30  // String implements the fmt.Stringer interface.
    31  func (c *Constant) String() string {
    32  	return c.Value.String()
    33  }
    34  
    35  func (c *Constant) ReturnType() types.T {
    36  	return c.Value.Type()
    37  }
    38  
    39  func (c *Constant) Eval(stmtCtx *stmtctx.Context, input datum.Row) (datum.Datum, error) {
    40  	return c.Value, nil
    41  }